The remarkable faith of the Ninevites is related to have been manifested about these times. That town, founded of old by Assure, the son of Sem, was the capital of the kingdom of the Assyrians. It was then full of a multitude of inhabitants, sustaining one hundred and twenty thousand men, and abounding in wickedness, as is usually the case among a vast concourse of people. God, moved by their sinfulness, commanded the prophet Jonah to go from Judæa, and denounce destruction upon the city, as Sodom and Gomorrha had of old been consumed by fire from heaven.
But the prophet declined that office of preaching, not out of contumacy, but from foresight, which enabled him to behold God reconciled through the repentance of the people; and he embarked on board a ship which was bound for Tharsus, in a very different direction. But, after they had gone forth into the deep, the sailors, constrained by the violence of the sea, inquired by means of the lot who was the cause of that suffering. And when the lot fell upon Jonah, he was cast into the sea, to be, as it were, a sacrifice for stilling the tempest, and he was seized and swallowed by a whale— a monster of the deep.
Cast out three days afterwards on the shores of the Ninevites, he preached as he had been commanded, namely that the city would be destroyed in three days, as a punishment for the sins of the people. The voice of the prophet was listened to, not in a hypocritical fashion, as at Sodom of old; and immediately by the order, and after the example, of the king, the whole people, and even those infants newly born, are commanded to abstain from meat and drink: the very beasts of burden in the place, and animals of different kinds, being forced by hunger and thirst, presented an appearance of those who lamented along with the human inhabitants.
In this way, the threatened evil was averted. To Jonah, complaining to God, that his words had not been fulfilled, it was answered that pardon could never be denied to the penitent.
Source: Sacred History (New Advent)